Torque pulse dampener

ABSTRACT

A torsional pulse dampener including a pulley rotationally coupled to a piston that is axially displaceable and adapted to give torsional compliance from an engine for at least one-half revolution of an angular differential displacement between the pulley and the piston.

PRIORITY CLAIM

This application claims priority to U.S. Provisional Application No.61/359,860 entitled “Power Plant, Torque Pulse Dampener, and Method ofUsing a Bypass Valve” filed Jun. 30, 2010.

BACKGROUND

1. Technical Field

The invention relates to torque pulse dampeners.

2. Description of Related Art

Vehicles consume significant amounts of fossil fuels. Due to limitedresources and environmental pressures, vehicle manufacturers areattempting to reduce fuel consumption of the vehicles they manufacturewhile still providing sufficient power. Superchargers and turbochargerscan be used to increase the power of an internal combustion engine. Aparticular system can include a combination of a supercharger, aturbocharger and turbo-compounding, using a hydraulic or mechanicalcontinuously variable transmission to drive the turbocharger up to aspecific speed or intake manifold pressure and then holding the speed tokeep it at a desired boost pressure for the engine condition. Such asystem relies on the supercharger to initially increase the boostpressure before the turbocharger can achieve sufficient boost pressure.

The application of Continuously Variable Transmissions (CVTs) tovehicular applications may also be used to improve fuel efficiencies bymaintaining a variable but preferred drive ratio between an internalcombustion engine and the driven load. In vehicular applications CVTdrives may be used in the transmission drive line between the engine andthe vehicle's wheels or in the drive line between the engine and variousaccessories. However applied, a CVT may be controlled by signals from acontrol module incorporating a software program that takes real-timeoutput values from a number of sensors measuring various relatedparameters. The computed CVT control signals would then effect CVT ratiochange by means of a servo actuator physically driving the input to theCVT's ratio-shift system.

Rolling traction CVTs rely on the “frictional” contact between rollingelements to transmit torque through their spinning input/output shafts.The force that effectively loads the contact surfaces between rollingelements within the CVT is often referred to as the normal force. Thenormal force allows the CVT to transmit tractive force (the torque beingtransmitted by the CVT). In rolling traction and similar CVTs, typicallylubricated and cooled by traction fluid, the normal force is typicallyseveral times greater than the tractive force. The exact relationshipbetween the normal and tractive forces varies with the specific design,operating conditions, temperature and type of traction fluid used. Ifthe ratio of normal force to tractive force is too low, then slip mayoccur and damage to the CVT's precision tractive surfaces may result. Ifthe ratio of normal force to tractive force is too high, then the CVT'sefficiency may be compromised and the CVT's service life will bedisproportionally reduced.

The ratio of normal to tractive forces may vary significantly inpractice due to a variety of torque variations. For example, the torquepulsations caused by the firing impulses of an internal combustionengine create cyclic angular accelerations on the rotating crankshaft.While the output from an internal combustion engine is usually specifiedin terms of mean torque, the pulse peaks may be several times the meantorque value. These variations can create temporary conditions where theratio of normal to torque forces in a connected CVT may be too low orhigh, creating the issues described above.

Other types of torque variation conditions often occur during theoperation of an engine. For example, in the case of an engineincorporating a supercharger driven from the engine's crankshaft, asudden demand by the driver for a high power output for briskacceleration would generate a sudden increase in torque as thesupercharger is engaged. Due to these types of torque variations, partsin the driveline are often sturdily designed to handle these types ofvariations in addition, a variety of types of damping mechanisms havebeen developed to help manage these variations.

These torque variations have implications to the use of CVTs or othertypes of transmissions or accessories such as superchargers andturbochargers with internal combustion or reciprocating engines ingeneral.

SUMMARY

A torsional pulse dampener including a pulley rotationally coupled to apiston that is axially displaceable and adapted to give torsionalcompliance from an engine for at least one-half revolution of an angulardifferential displacement between the pulley and the piston.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures maybe exaggerated or minimized relative to other elements to help toimprove understanding of embodiments of the invention. Embodimentsincorporating teachings of the present disclosure are illustrated anddescribed with respect to the drawings presented herein.

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, further objectivesand advantages thereof, as well as a preferred mode of use, will best beunderstood by reference to the following detailed description ofillustrative embodiments when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a schematic view of embodiments of a power plant and systemhaving a CVT for modulation of power output;

FIG. 2 is a schematic plan view of other embodiments of a power plant;

FIG. 3 is a schematic diagram of an embodiment of a powertrain systemfor FIGS. 1 and 2;

FIGS. 4 and 5 are schematic views of other embodiments of power plants;

FIG. 6 is a high level flow diagram of an embodiment of a control systemfor the power plant;

FIG. 7 is an enlarged sectional view of an embodiment of a CVT andtorque pulse dampener assembly;

FIG. 8 is an isometric, partially-sectioned view of another embodimentof a pulse torque dampener;

FIG. 9 is a reverse isometric, partially-sectioned view of theembodiment of the dampener of FIG. 8;

FIG. 10 is an isometric view of an embodiment of a shaft for thedampener of FIG. 8;

FIG. 11 is an isometric view of an embodiment of a piston for thedampener of FIG. 8;

FIG. 12 is a partially-sectioned side view of portions of the embodimentof the dampener of FIG. 8;

FIG. 13 is a partial-sectioned isometric view of an embodiment of a sealfor the dampener of FIG. 8;

FIG. 14 is a sectional side view of another embodiment of a dampener;

FIG. 15 is an isometric view of another embodiment of a torque pulsedampener;

FIG. 16 is a partially-sectioned, isometric view of an embodiment of thedampener of FIG. 15;

FIG. 17 is a reverse, partially-sectioned, isometric view of anembodiment of the dampener of FIG. 15;

FIG. 18 is a partially-sectioned side view of embodiments of internalcomponents of the dampener of FIG. 15; and

FIG. 19 is a schematic diagram of another embodiment of a powertrainsystem.

FIG. 20 is a flowchart showing the operation of a bypass valve inaccordance with the FIGS. above.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION

The following description in combination with the figures is provided toassist in understanding the teachings disclosed herein. The followingdiscussion will focus on specific implementations and embodiments of theteachings. This focus is provided to assist in describing the teachingsand should not be interpreted as a limitation on the scope orapplicability of the teachings. However, other teachings can certainlybe utilized in this application. The teachings can also be utilized inother applications and with several different types of systems andassociated components.

Devices that are in operative communication with one another need not bein continuous communication with each other unless expressly specifiedotherwise. In addition, devices or programs that are in communicationwith one another may communicate directly or indirectly through one ormore intermediaries.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of features is notnecessarily limited only to those features but may include otherfeatures not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive-or and not to an exclusive-or. For example,a condition A or B is satisfied by anyone of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

Also, the use of “a” or “an” is employed to describe elements andcomponents described herein. This is done merely for convenience and togive a general sense of the scope of the invention. This descriptionshould be read to include one or at least one and the singular alsoincludes the plural, or vice versa, unless it is clear that it is meantotherwise. For example, when a single device is described herein, morethan one device may be used in place of a single device. Similarly,where more than one device is described herein, a single device may besubstituted for that one device.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of embodiments of the present invention, suitablemethods and materials are described below. In addition, the materials,methods, and examples are illustrative only and not intended to belimiting.

Embodiments of power plants, torque pulse dampeners, and methods ofusing bypass valves are disclosed. This detailed description begins witha brief overview and a more detailed discussion follows.

In a set of embodiments, a power plant can include an internalcombustion (IC) engine having a crankshaft, a pump coupled to the ICengine, and a continuously variable transmission (CVT) coupled to thecrankshaft and the pump. The CVT has a control ratio operable to controla pressure of a compressible fluid provided from the pump to the ICengine, wherein the control of the pressure extends in a range from avacuum pressure to another pressure higher than atmospheric pressure.

In another set of embodiments, a power plant can include an engine, acontinuously variable transmission (CVT), and a torque pulse dampener(TPD) coupled to the engine and to the CVT.

In a further set of embodiments, a torsional pulse dampener can includea pulley rotationally coupled to a piston that is axially displaceableand adapted to give torsional compliance from an engine for at leastone-half revolution of an angular differential displacement between thepulley and the piston.

In yet a further set of embodiments, a method of controlling a valve ofa pump comprises operating an engine having an engine intake coupled toa pump output of a pump, and a continuously variable transmission (CVT)coupled to the engine and to the pump; and operating a valve between apump input of the pump and the engine intake, such that the valve can beopened during a ratio change of the CVT.

The foregoing and other objects and advantages of the embodiments willbe apparent to those skilled in the art, in view of the followingdetailed description, taken in conjunction with the appended claims andthe accompanying drawings.

A power plant can include an engine and a continuously variabletransmission (CVT) coupled directly or indirectly to the engine. The CVTcan be any of several types, many of which will be described later inthis specification. In a particular embodiment, the CVT is a rollingtraction CVT, and more particularly, a Milner-type CVT. The CVT caninclude planetary members in rotting contact with axially movable innerand outer races. In an embodiment, the engine is an internal combustion(IC) engine having a crankshaft. The crankshaft can be coupled directlyor indirectly to the CVT, which in turn can be coupled to a pump,accessory, or the like.

In a particular embodiment, the pump can be a positive displacementcombined pump and motor (PDCPM) and can compress a compressible fluid,such as a gas. In a particular embodiment, the pump is a supercharger.The gas can include air, O2 (for example, at a concentration other thanair), H2, a methane-containing or ethane containing gas (for example,natural gas), N2O, CO, another suitable gas used by an IC engine, or anycombination thereof. The CVT has a control ratio that can control thepressure of the gas or other compressible fluid provided from the pumpto the engine over a range from a vacuum pressure to another pressurehigher than atmospheric pressure.

In some embodiments, the pump has a pump output that is coupled to anengine intake of the engine. An intake manifold can be coupled to thepump output and the engine intake. A valve can be implemented along theflow path between the pump and the engine. In another embodiment, eachcylinder may have its own separate intake, rather than the intakemanifold.

In another particular embodiment, the accessory can include analternator or a pump, such as a water pump, a power steering pump, anair conditioning compressor, or the like. In another embodiment, thepower plant can include a torque pulse dampener (TPD) that can becoupled to the engine and the CVT.

Skilled artisans will appreciate that many engines use a liquid fuelsource and use air as an oxygen source. To simplify understanding of theconcepts described herein, a particular power plant having an IC enginewherein the pressure of air supplied to the IC engine is controlled isdescribed. After reading this specification, skilled artisans willappreciate that other compressible fluids may be used in place of or inconjunction with air. To the extent oxidizing gases and fuel-based gaseshave different concerns, such concerns will be addressed with respect toparticular components, for example, the bypass valve.

Referring to FIGS. 1 and 2, for example, a power plant 21 may comprisean engine 23, a continuously variable transmission (CVT) 41 and a torquepulse dampener (TPD) 71 coupled to the engine 23 and the CVT 41. The TPD71 dampens torque pulses between the engine and the CVT. Embodiments mayfurther comprise an accessory 43 (e.g., a pump, an alternator, etc.)coupled to the engine 23, with the CVT coupled to the engine and theaccessory, and the CVT having a control ratio operable to control aninput from the engine to the accessory. As shown in FIG. 3, the engine23 may form a portion of a powertrain system including a transmission 72coupled thereto and adapted to change gears to distribute power to awheel of a vehicle having the power plant. The transmission may have aplurality of fixed ratios.

An embodiment of power plant 21 includes an IC engine 23 having acrankshaft 25 (FIGS. 1 and 2). A pump 43 is coupled to the IC engine 23.The CVT 41 is coupled to the crankshaft 25 and the pump 43. The CVT 41has a control ratio operable to control a pressure of a gas or fluidprovided from the pump 43 to the IC engine 23. The control of thepressure extends in a range from a vacuum pressure to another pressurehigher than atmospheric pressure.

Other embodiments of the power plant 21 comprise an IC engine 23 havingcrankshaft 25, a crankshaft pulley 27 mounted to the crankshaft 25 fordriving at least one accessory belt 29. Belt 29 may be used to drivevarious accessories, such as an air conditioning compressor 31, analternator 33, a water pump 35, etc., and may be routed through an idler37.

Belt 29 also is coupled to a continuously variable transmission (CVT)41, either directly or indirectly. The CVT 41 is positioned between andcoupled to the crankshaft 25 and pump 43. In some cases, pump 43 may bea positive displacement combined pump and motor (PDCPM), such as asupercharger. For the purposes of this specification, a turbocharger isnot a type of supercharger. The CVT 41 has an output shaft 45 thatdrives the pump 43 through an optional coupling 47, such as a compliantcoupling. The pump 43 has an engine intake 49 and a pump output 51 thatfeeds processed air into an intake manifold 53 that is coupled to ICengine 23.

The outlet 51 may further comprise a bypass connection 55 as part of theintake system between the intake manifold 53 and atmosphere. The bypassconnection 55 may be located along a flow path between the engine intakeand atmosphere, the embodiments of FIGS. 4 and 5, the bypass connection55 may be selectively opened, closed or modulated with a valve 58. Thevalve 58 may be located along the flow path at a point between theengine intake 49 and the pump output 51, wherein the valve 58 isoperable to open, close or modulate the bypass connection 55. The valve58 also may be located in or between the pump output 51 and the intakemanifold 53 that provides air for cylinders of the IC engine 23. Inparticular embodiments, the valve 58 can be a pressure relief valve orwaste gate valve, a fast acting butterfly valve, etc.

The system may further comprise an engine throttle 56, an air mass flowsensor 60 and an exhaust gas sensor 62. These embodiments also maycomprise sensors 64, such as a temperature sensor, a pressure sensor orany combination thereof. The sensors 64 may be use in an operationalcontrol system, such as the control system 101 depicted in FIG. 6 whichwill be described later herein.

In some embodiments, the pump 43 comprises a supercharger having thevalve 58. The valve 58 is normally used to release excess pressure so asto not exceed the maximum pressure rating of the system components. Whenthe CVT 41 is used to operate the supercharger, it is desirable to shiftthe system as quickly as possible to attain maximum boost within a shorttime window. For example, in some embodiments the operations used forthis rapid shift time are:

Opening the valve 58 to release the boost pressure that would otherwisebe fed to the engine 23;

Shifting the CVT 41 to a desired control ratio (either increasing thecontrol ratio or decreasing the control ratio) as fast as desired, underlow load conditions, such that a smaller shift force is exerted on theCVT system; and

Closing the valve 58 to regain or rebuild boost pressure in the pump 43so that engine boost is reestablished.

Because shifting is performed under relatively low loading conditions, asmall shift motor 44 may be used to control the CVT 41.

Alternatively, this system and method for rapid shifting may comprise apulsed operation of the valve 58. The pulsed operation of valve 58allows the pressure to be released in a controlled method to achieve therapid shift (again, low to high, high to low, or any control ratiosbetween low and high) without completely releasing all of the engineboost pressure. This embodiment provides better engine performance asthe complete boost is not released, and the CVT 41 shifts at a nominalshift force level while still attaining the desired rapid shift time.

In yet a further set of embodiments, a method of controlling a valve ofa pump operating with an engine and CVT can have the engine intakecoupled to a pump output, with the CVT coupled to the engine and to thepump. In some examples, the force used to change the ratio of the CVT isa function of the torque imposed on the CVT, such that lowering thetorque also towers the ratio change force. In some embodiments, a valvebetween the pump output and pump input is opened and closed to vary thedifferential pressure across the pump resulting in lowering orincreasing the torque used to drive the pump. This control methodpermits greater ratio control speed or a reduction in control force forthe CVT.

The method also may comprise operating a valve between a pump input ofthe pump and the engine intake, such that the valve can be opened duringa ratio change of the CVT. Otherwise the valve is closed in part or inwhole. Operating the valve may comprise increasing a pressure at a pointalong a flow path between the pump output and the engine intake; openingthe valve to decrease the pressure at the point along the flow pathbetween the pump output and the engine intake during the ratio change tochange a shift torque exerted on the CVT; and closing the valve afterthe ratio change.

Other embodiments increasing a pressure at a point along a flow pathbetween the pump output and the engine intake; opening a valve todecrease the pressure at the point along the flow path between the pumpoutput and the engine intake; changing the CVT to a different controlratio such that a tower shift force is exerted on the CVT; and closingthe valve after changing the CVT to the different control ratio. Closingthe valve regains pressure in the pump so that an engine boost pressureand load on the CVT are reestablished. Changing the CVT to a differentcontrol ratio occurs temporarily under lower loading conditions suchthat the lower shift force is exerted on the CVT. The CVT changescontrol ratios within a range of about 0.1 to 0.5 seconds, or about 0.3seconds in some embodiments. The valve has a response time of about 0.05to 0.1 seconds, or about 0.08 seconds in some embodiments.

Opening the valve may include pulsing an operation of the valve to allowthe pressure to be released therethrough in a controlled method withoutcompletely releasing all of the pressure. A solenoid valve may be usedto control pneumatic vacuum to the bypass valve of the pump. A signalfrom an engine controller may be used to modulate an air volume to thebypass valve and thereby control a position of the valve.

In some embodiments, the control ratio of the CVT 41 is changed within afraction of a second, and the valve 58 has a response time ofmilliseconds, as described previously herein. In addition, someembodiments use a solenoid valve 66 (FIG. 4) to control the pneumaticvacuum to the valve 58. A signal from an engine controller 103 (FIG. 6)may be used to modulate the air volume to the valve 58 and thus controlthe position of the valve 58. This embodiment obtains improved boostpressure for faster shift responses.

Embodiments of the CVT 41 have a control ratio that provides a primarycontrol to modulate a power of the engine over a range from a towatmospheric intake manifold pressure to an elevated boost level aboveatmospheric pressure. The low atmospheric intake manifold pressure maybe below atmospheric pressure. For example, in some embodiments the CVTcontrol ratio is continuously variable over a turndown range ofapproximately 6:1 to 10:1, and 8:1 in some embodiments. This results ina range of pressures from about 0.15 to 1.5 atmospheres (absolute). Forexample, the low atmospheric intake manifold pressure may be about 0.17atmospheres (absolute) at idle of the engine, and the elevated boostlevel may be about 1.4 atmospheres (absolute) at full power of theengine. At low power outputs typical of low and mid-speed operations,this solution provides a more nearly adiabatic expansion of the intakeair that is fed to the cylinders compared with the near-isothermalconditions attributable to throttling.

In some embodiments, the CVT 41 may comprise a toroidal CVT, asemi-toroidal CVT, or a rolling traction CVT. Embodiments of CVT 41 alsomay comprise a rolling traction CVT of a Milner type, which is alsoknown as a Milner CVT or MCVT. See, e.g., U.S. Pat. No. 7,608,006, whichis incorporated herein by reference in its entirety. The CVT 41 may besingle-stage and have a single set of races and planets, or more thanone stage and have more than one set of races and planets coupled inseries, to extend a range of the CVT control ratio. Alternatively, andas schematically depicted in FIG. 2, the CVT 41 may comprise two or moreCVTs, such as different types of CVTs 41 a, 41 b coupled in series.

In the illustrated embodiment of FIG. 7, the CVT 41 comprises a variableplanetary ball CVT having planetary members 61 in rotting contact withaxially movable inner and outer races 63, 65 and a carrier 67 havingfollowers 69. Embodiments of the CVT 41 may comprise metal-to-metal orceramic traction surfaces that are adapted to be lubricated and cooledby a fluid.

Again referring to FIG. 6, a high level flow diagram of an embodiment ofa control system 101 for the power plant 21 is shown. For example,control system 101 may comprise a controller 103, such as amicroprocessor or engine controller (or any combination thereof) thatreceives input signals for manifold temperature 105, manifold pressure107, engine speed 109, pump speed 111, input demand 113 (e.g., the gaspedal of the vehicle), and a fuel efficiency map 115. Controller 103then outputs control signals for the engine ignition 117, fuel injection119, engine throttle 121, pump bypass 123, CVT actuator 125 and CVT 127,or any combination thereof. As discussed herein, the CVT 127 drives thepump speed 111.

Attention is now directed to details of the TPD. Although many TPDs canbe used in the foregoing powerplant embodiments, particular TPDs may bebetter suited for use with such powerplant embodiments.

The peak-to-mean torque pulsations caused by the firing impulses of anIC engine superimpose angular accelerations on the rotating crankshaft,and my even excite torsional resonance in the crankshaft at particularengine speeds. When the drive to the pump is taken from the front of thecrankshaft where these accelerations are typically at their highest, theangular accelerations react to the inertia of the driven system ascyclic torsional pulses. Further, the system as a whole may exhibit adynamic response greatly exacerbating the torsional loads. The size anddurability of a planetary rolling traction CVT is sensitive to the peaktorsional loads imposed upon it. Accordingly, and as depicted throughoutthe illustrated embodiments, these cyclic pulses can be reduced by a TPD71 positioned in the driveline between the engine crankshaft and theinput drive to the CVT.

There are a number of commercially available torsional damping devicesto address this condition for driven engine accessories such asalternators. These devices, however, typically incorporate compliantelements that are tuned to the fixed polar moment of inertia of thedriven accessory. When a ratio change mechanism is incorporated betweenthe engine crankshaft and driven accessory, the mean torque that thecompliant element reacts to changes proportionally, as does theeffective polar moment of inertia of the driven system. Conventionaldecouplers may be limited in function across the full operating range ofthe CVT. This can be detrimental to the successful application oftoroidal and rolling traction CVTs since the reaction of torsional pulseloads can shorten the life of the CVT and can cause failure.

To address more fully these cyclical torsional pulsation effects with atorsionally damped, torsionally compliant element, significant angularcompliance of the element may be used at full torsional load. This mayrepresent more than one revolution of differential displacement,depending on the system configuration and loading. Accordingly, one typeof pulse mitigation device or TPD 71 incorporates an axially displacedpiston to give torsional compliance for up to a plurality of revolutions(e.g., one, two or three revolutions), if desired. This embodiment alsomay incorporate a variable rate spring and a damped movement.

The foregoing device that reduces or mitigates engine crankshaft cyclicpulsations is different from or additional to any torsionally compliantdevice (e.g., compliant coupling 47 in FIG. 1) fitted between the CVTand a pump input shaft whose purpose is to reduce or mitigate thetypically lesser effects of cyclic drive torque pulsations oftencharacteristic of supercharger input drives.

Accordingly, a connection between the CVT 41 and the crankshaft 25 maybe made with at least one gear, shaft, rolling traction drive, belt orchain, or any combination thereof. Embodiments of the connection betweenthe CVT 41 and the crankshaft 25 may comprise the TPD 71. TPD 71 may bedriven by a pulley and positioned between and coupled to the crankshaft25 and the CVT 41 to provide torsional compliance or torsionalcompliance and damping.

While cyclical torque pulse dynamics are relatively easy to understandand model, practical methods of mitigating torque effects in realsystems have proven far less attainable. One solution that permits aplurality of complete turns of angular displacement within a compactembodiment is to change the direction of displacement of the spring anddamped elements from angular to axial. Spiral splines with more than onestart and viscous hydraulic damping may be employed as a simpler,inexpensive solution. Embodiments provide a sealed unit that is suitablefor use as a CVT drive, an alternator dampener and still otherapplications.

For example, embodiments of a system, method and apparatus for a torquepulse dampener for front end accessory drives and engine accessoriesdriven by CVTs are disclosed. One embodiment of a torque pulse dampenerfor an automotive alternator has a pulley diameter of about 50 mm and amaximum rotational speed of about 12,000 rpm, with a peripheralcentripetal loading of about 4,000 g.

In the embodiment of FIGS. 8-13, the TPD 71 has a shaft 601 that ishollow, central and coupled to, for example, the drive shaft 603 (FIG.8) of a mechanical device or accessory (e.g., an alternator) via aninternally splined connection 605 and nut. The shaft 601 is furnishedwith substantial involute splines 607 on its exterior as well. In theembodiment shown, the splines 607 are truly axial, but also may comprisea shallow helix with respect to the axis. A slightly helical shape maybe used to modify the drive torque spring and damping function.

A piston 609 slides freely onto the splines 607 of shaft 601 in an axialmotion such that piston 609 encircles a first portion of shaft 601. Thepiston 609 has mating internal axial splines 611 (FIG. 11) that transmita drive torque to the central shaft 601. This provides an output driveto the shaft 603 of the device to which it is attached. In theembodiment shown, the piston 609 has on its exterior dual start involuteor spiral threads 613, such as buttress or involute form threads. Thedual start threads 613 engage matching internal spiral threads 615 inthe pulley housing 617.

Embodiments have a pair of full compliment, angular thrust bearings 621,622 that are located between the housing 617 and piston 609. Thus,without the piston 609 in place, the outer pulley 623 may not drive theinner shaft 601. In the embodiment of FIG. 8, housing 617 is anextension of outer pulley 623. With the piston 609 in place, however,angular rotation of the outer pulley housing 623 about its axis relativeto the inner shaft 601 causes the piston 609 to axially traverse theinner shaft 601 in either axial direction. When the outer pulley housing623 rotates in one direction, the piston 609 moves into abutment withthe bearing 621. If pulley 623 is rotated in the other direction, thepiston 609 moves axially toward the open end (right side in FIG. 8) ofthe assembly. Under drive torque it is desirable to move the piston 609toward the open end.

Embodiments of the second angular thrust bearing 622 are in oppositionto the first bearing 621 to constrain the inner shaft 601 to the outerpulley 623. The pair of bearings 621, 622 only can move in rotation orangular displacement relative to each other. The piston 609 isconstrained to move only axially if the outer pulley housing 623 isrotated relative to the inner shaft 601.

When the piston 609 moves axially toward the end (e.g., left to right inFIG. 8), the piston 609 bears on a spring 625, such as a stack ofbellville springs. As shown in FIG. 8, spring 62 is arranged along asecond portion of shaft 601 adjacent piston 609. The spring 625 itselfis prevented from being displaced (e.g., toward the right in FIG. 8) bya flange 602 at the end of inner shaft 601. Thus, a torque applied tothe outer pulley housing 623 against a counter-torque applied to theinner shaft 601 results in an axial displacement of the piston 609against the force of the spring 625. In so doing, the outer housing 617is angularly displaced, for a plurality of revolutions if necessary,against a predefined, increasing torsional resistance. The torsionalresistance is a defined function of the configuration of the spring 625,and may be linear or non-linear in function. Further, the torsionalcompliance may be reconfigured for a variety of applications merely byselecting springs 625 having appropriate parameters.

In some embodiments, such as those that are used to transmitbi-directional (i.e., clockwise and counterclockwise) torque, a secondcompliant element, such as a spring, elastomer or Belleville washer,spring or stack, may be additionally fitted to the opposite end ofpiston 609 from spring element 625 along a third portion of shaft 601.Such an additional spring element is shown as spring 506 along a thirdportion of inner shaft 525 in FIG. 14.

In some embodiments, the damping function of the TPD 71 is achieved bypartially filling the cavity between the inner shaft 601 and the housing617 of the outer pulley 623 with a lubricant or oil of a predefined andcontrollable viscosity. Suitable lubricants include those that haveviscosities that are substantially insensitive to temperature change.

Embodiments of the lubricant and damping fluid may be permanently sealedin place by seals 631 at each end of the pulley housing and inner shaft.Oil seals 631, which are depicted in FIG. 13 as being energized byelastomer o-rings 633, have their moving contact to their outerperiphery. The sealing contact pressure is intensified by the highcentripetal forces, rather than being depleted by it. Typical sealmaterials may comprise a variety of suitable polymers or compositematerials. Further, the frictional contact between the seals and theirrespective sealing surfaces may be used as an intrinsic part of thedamping action of the device.

Again referring to FIGS. 8 and 9, some embodiments of the angularcontact bearings 621, 622 may be preloaded against each other with athrust race, such as at least one additional (e.g., stiff) Bellevillespring 627 that pushes the inner races firmly against the outer races.Preloading is used because of the high angular accelerations imposed bythe torsional pulsing. Preloading also reduces slippage of the balls andwear caused by its reaction against the inertia of the balls in thebearings. Accordingly, the balls are designed to roll rather than slide.Furthermore, the preload spring also facilitates assembly of the unit,which is otherwise swaged permanently together and sealed for life insome embodiments. The torque pulse dampener also may be configured suchthat the locations of the springs are reversed. Either way, the dampingprovided by the lubricant is in both axial directions as the oil ispumped.

As shown in FIGS. 7 and 14-18, embodiments of the TPD 71 may comprise,for example, an axially-displaced piston 503 encircling a first of innershaft 525 (FIG. 14) to give torsional compliance for more than onerevolution of differential displacement, and a spring 505, such as avariable-rate Belleville spring, arranged along a second portion ofinner shaft 525 adjacent piston 503 to provide a damped movement.Together, the CVT 41 and TPD 71 may comprise an assembly.

A pulley 501 is rotated by belt 29 as described herein and rotates abouta housing 507 via sealed thrust races 509. The pulley 501 is coupled toa recirculating ball system that axially drives the piston 503. Thepiston 503 acts as a ball nut for, e.g., two sets of balls 513 (FIG. 18,only one shown, for ease of understanding seated in the dual-startthreads 515 on the exterior of the piston 503. The balls 513 also engagecomplementary threads 517 on the interior of pulley end caps 519. Thisembodiment provides the recirculating ball system for translating therotational motion of the pulley 501 to axial motion of the piston 503.Alternatively, the threads 515 may comprise one start threads with oneset of balls, or three-start threads with three sets of balls.

As shown in FIG. 14, the pulley 501 and piston 503 may engage viacomplementary, dual-start involute or spiral threads 516, 518, such asthose described herein for the embodiment of FIG. 8. Similarly, thepiston 503 may comprise internal splines 521 that axially engageexternal splines 523 on an inner shalt 525. Thus, inner shaft 525 andpiston 503 are locked in rotation together, but piston 503 is permittedto move axially with respect to inner shaft 525.

The axial motion of piston 503 draws in oil or lubricant from areservoir, for example the CVT traction fluid lubricant, through one-wayinlet valves 527 (FIG. 15), which have inlet valve balls 529 (FIG. 16)biased radially inward by springs 531. In some embodiments, oil dampingis asymmetrically provided only when piston 503 moves left to right.Spring 505 provides damping when piston 503 moves right to left. In FIG.14, however, spring 506 provides additional damping for piston 503, butalso may be equipped with inlet valves 527 for oil damping. Springs 505,506 may comprise Belleville springs or other spring elements, such aselastic elements. When TPD 71 is coupled to CVT 41 by carrier 67 (FIG.7), fluid may be communicated via an outlet reed valve. Thus, the TPDmay be damped with lubricant between a shaft, a piston and a housing ofthe TPD. Lubricant damping of the piston may be symmetrical in bothaxial directions, or asymmetrical such that it is damped in only oneaxial direction, and spring damping is provided in the other axialdirection.

In general, TPD 71 may be coupled to a rotating element of CVT 41, suchas output shaft 45, inner races 63, outer races 65, carrier 67 orfollowers 69 to reduce cyclic torsional pulses between CVT 41 and engine23. It will be appreciated that the roles of inner races 63, outer races65, and the combination of carrier 67 and followers 69 (as planets), areall interchangeable so that any one of them may be held stationary andthe other two used either as the input or the output member of CVT 41.Again referring to FIGS. 4 and 5, alternate embodiments of CVT and TPDlayouts are depicted. Embodiments of the torsional pulse mitigationdevices depicted herein may be reconfigured for either of these designs.In FIG. 4, the TPD 71 is configured as a coaxial pulse mitigator locatedbetween the CVT 41 and pump 43, and the output shaft passes through theTPD 71 unimpeded. In such an embodiment, the output of the TPD may, insome cases, be used to drive the carrier 67 of the CVT 41 as shown inFIG. 7. The CVT 41 may be actuated by, for example, a CVT ratio changeservo motor 44. In FIG. 5, an in-line pulse mitigator configuration hasthe CVT 41 between the TPD 71 and the pump 43, and again operated by aCVT ratio change servo motor 44.

In other embodiments, the TPD is coupled to the crankshaft and the CVTfor dampening torque pulses between the IC engine and the CVT. The TPDmay comprise a pulley coupled to the crankshaft via a belt and adaptedfor rotation therewith, wherein the pulley rotationally engages andaxially displaces a piston within the TPD to give torsional compliancefrom the IC engine for at least one-half revolution of angulardifferential displacement between the pulley and the piston. The pulleyrotationally engages the piston with a ball screw or buttress threads.The TPD may comprise a variable-rate Belleville spring and a dampedmovement for the piston. The TPD is located between the pump and the CVTsuch that the CVT has an output that extends through the TPD to thepump, or the CVT is located between the pump and the TPD. An output ofthe TPD drives a carrier of the CVT, and the CVT is actuated by a CVTratio change servo motor.

The TPD may have a shaft coupled to a drive shaft of the pump via aninternally splined connection, the shaft also having splines that areexternal and involute. The piston is axially movable on the shaftsplines, the piston also having threads on an exterior thereofcomprising dual-start involute or spiral threads, a pulley threadinglymounted to the threads of the piston, and the pulley is coupled to thecrankshaft. Angular rotation of the pulley about an axis relative to theshaft causes the piston to axially traverse the shaft in either axialdirection. A first angular thrust bearing between a housing of thepulley and the piston physically constrains the shaft to the pulley. Asecond angular thrust bearing is in opposition to the first angularthrust bearing, wherein the first and second angular thrust bearings arelimited to rotational or angular displacement relative to each other,such that the piston is physically constrained to move onlysubstantially axially when the pulley is rotated relative to the shaft.The first and second angular thrust bearings may be preloaded againsteach other with a thrust race.

A spring may be located between the housing and the piston for axiallyrestraining the piston, wherein a torque applied to the pulley against acounter-torque applied to the shaft axially displaces the piston againstthe three of the spring, such that the housing is angularly displacedagainst an increasing torsional resistance defined by the spring.Angular displacement of the housing may comprise at least one-half orone revolution relative to the piston. The pulley may be coupled to arecirculating ball system that axially drives the piston, the pistonacts as a ball nut for at least one set of balls seated in threads on anexterior of the piston, and the balls engage complementary threads on aninterior of the pulley for translating the rotational motion of thepulley to axial motion of the piston.

The TPD embodiments disclosed herein have numerous advantages. If drivetorque is needed, it provides significant angular displacement of about1.5 turns or more. This exceeds the displacement of conventionaldevices, which are limited to no more than about one-quarter turn.Moreover, these TPD embodiments convert rotation to linear displacementto achieve greater angular displacement with a ball screw or threadscrew. The ramps on the housing and piston are used for axialdisplacement.

In one embodiment, the TPD is well suited for dampening applicationshaving large torque pulses, such as engines with low cylinder counts(e.g., one-cylinder all terrain vehicle (ATV) engines). For example,FIG. 19 schematically depicts an embodiment of a powertrain ordrivetrain system including a transmission 72 for the drivetrain thatchanges gears to distribute power to a wheel of a vehicle having thepower plant. The transmission 72 may have a plurality of fixed ratios.The CVT 41 and TPD 71 may be coupled between the engine 23 andtransmission 72 to mitigate torque pulses from the engine 23 to thetransmission 72.

FIG. 20 is a flowchart showing the operation of a bypass valve inaccordance with the FIGS. above. In a first step 900, the engine isstarted and air begins to flow through the engine intake manifold. In asecond step 910, the supercharger or turbocharger pump is engaged andsends higher pressure air to the engine intake manifold. In a third step920, the engine speed increases whereby the pump increases the pressureof the air to the engine intake manifold, generally in response to anoperator demanding greater speed by depressing a throttle. In a fourthstep 930, this increased demand may create a ratio change in the CVT asthe system responds to these demands.

In a fifth step 940, control software determines whether the airpressure or temperature exceed certain limits acceptable during a ratiochange. If yes, then in step 950, a bypass valve is temporarily openedto decrease the pressure and or temperature within the engine intakemanifold. The bypass valve may be a fully opened, partially opened, orfully opened intermittently such as with pulse modulation. Once theratio change has completed or if the pressure and temperature within theengine intake manifold have fallen within specification, then the bypassvalve is closed and processing continues to step 960. If not in step940, then in step 960 the engine proceeds operating until the driverdemands another speed increase or a speed decrease or turns off theengine.

The following is an example of modeling an embodiment of an internalcombustion engine furnished with a positive displacement superchargerdriven from the engine's crankshaft via a CVT as described above. Theinput variables are RPM engine=700, CVT ratio=7, CVT efficiency=0.87, SCtorque=30 Nm, and SC pmi=7.44*10⁻⁴ Kg m2. With an engine firingfrequency at 2 pulses per revolution such as with a four cylinder fourstroke engine, Hz pulses=(RPM engine*2)/60=23.3. With a design frequencysufficiently below pulse frequency to avoid excitement Hz design=Hzpulse/2=11.7. The design period of oscillation is T design=1/Hzdesign=0.0857 sec. From the fundamental torsional pendulum relationshipT=(2*pi*(square root of (I/K)) where T=period of oscillation, I=polarmoment of inertia, and K=torsional constant. When rearranged in terms ofthe torsional constant K, K=4*pi squared*I/(T squared). Substituting theinput variables to give K at the CVT carrier input K coupling=4*(pisquared)*SC pmi*CVT ratio/(T design squared)=27.98. From the fundamentalrelationship T=−K*theta where T=driving torque and theta=angulardisplacement, rearranged in terms of theta becomes theta=−(T/K).Substituting the input variables, the angular displacement theta and thedrive torque in radians, theta=−8.63 rad or −494.195 degrees orapproximately 1.4 rotations due to the mean torque.

The methods and systems described herein overcome other attempts toimprove fuel efficiency, power, or other operational concerns. For agiven defined driving cycle, the fuel consumption of an automobile issignificantly dependent on vehicle mass, aerodynamic drag and rollingresistance drag. Advances in overall vehicle design to improve fuelefficiency have therefore commonly involved the reduction of weight,frontal area and aerodynamic coefficient of drag, as well as theoptimization of the drive train. However, such improvements may notsignificantly affect the performance of the power plant, for example anIC engine.

Selective cylinder deactivation is being considered by some automobilecompanies. However, this alternative tends to be limited to engines withthe larger number of cylinders, and have so far failed to impact thesmaller, four cylinder engine market directed toward fuel efficiency.

While some techniques reduce throttling losses, they have by no meanseliminated them. A typical modern engine still spends a very largeportion of its time running throttled. For example, during low tomid-speed operation, or coasting and idling in traffic, both of whichcomprise a significant portion of contemporary driving, the engine isstill running at least partially throttled.

Japanese Patent 1-110874, attempts to conceptually show how some energymay be reclaimed by using a hydraulically-controlled, belt-driven CVT.The execution of this design by means of a belt-driven CVT, with its lowefficiency, limited durability, and slow ratio-change response timerender it impractical. U.S. Pub. No, 2006/0032225 and WO 2010/017324disclose other conventional CVT solutions.

Thus, the methods and systems as described herein provide a moreuniversal solution to designing highly fuel efficient vehicles, ratherthan providing multiple tradeoffs between conventional approaches, suchas aerodynamics, selective cylinder deactivation, or less sophisticatedapproaches. The embodiments as described herein provide a synergisticapproach to design that seeks to combine complimentary technologies tobring a significant cumulative effect to address more fully the problem.In the field of fuel efficient automobile design and innovation thereare now some examples of this. While the embodiments described hereinprovide a better solution as compared to conventional approaches, theembodiments can be implemented with any one or more of the conventionalapproaches, such as improved aerodynamics, selective cylinderdeactivation, or the like. For example, TPD embodiments may allowsuperchargers or front end accessories to be used more effectively witha four cylinder engine, with or without selective cylinder deactivation.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed are not necessarily the order inwhich they are performed.

The specification and illustrations of the embodiments described hereinare intended to provide a general understanding of the structure of thevarious embodiments. The specification and illustrations are notintended to serve as an exhaustive and comprehensive description of allof the elements and features of apparatus and systems that use thestructures or methods described herein. Many other embodiments may beapparent to those of skill in the art upon reviewing the disclosure.Other embodiments may be used and derived from the disclosure, such thata structural substitution, logical substitution, or another change maybe made without departing from the scope of the disclosure. Accordingly,the disclosure is to be regarded as illustrative rather thanrestrictive.

Certain features are, for clarity, described herein in the context ofseparate embodiments, may also be provided in combination in a singleembodiment. Conversely, various features that are, for brevity,described in the context of a single embodiment, may also be providedseparately or in any subcombination. Further, reference to values statedin ranges includes each and every value within that range.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover any andall such modifications, enhancements, and other embodiments that fallwithin the scope of the present invention. Thus, to the maximum extentallowed by law, the scope of the present invention is to be determinedby the broadest permissible interpretation of the following claims andtheir equivalents, and shall not be restricted or limited by theforegoing detailed description.

What is claimed is:
 1. A torsional pulse dampener comprising: a hollowshaft comprising a first set of splines extending longitudinally alongan exterior surface of the hollow shaft; a piston encircling a firstportion of the hollow shaft, wherein the piston comprises a second setof splines extending longitudinally along an interior surface of thepiston, and wherein the second set of splines is slidingly mated withthe first set of splines; a first spring arranged along a second portionof the hollow shaft adjacent the piston to provide axial restraint ofthe piston; a pulley encircling at least a portion of the piston,wherein the pulley is threadingly mounted to the piston via respectivescrew threads comprising an interior surface of the pulley and anexterior surface of the piston such that the piston is axially displacedrelative to the pulley by rotation of the pulley; and one or more rotarybearings disposed within the torsional pulse dampener such that thepiston is axially displaced along the hollow shaft by rotation of thepulley.
 2. The torsional pulse dampener of claim 1, wherein the firstspring is a variable-rate spring.
 3. The torsional pulse dampener ofclaim 1, wherein the hollow shaft comprises a third set of splinesextending longitudinally along an interior surface of the hollow shaft.4. The torsional pulse dampener of claim 1, wherein the screw threadcomprising the exterior surface of the piston is a dual-start thread. 5.The torsional pulse dampener of claim 1, wherein the one or more rotarybearings comprise a pair of angular thrust bearings respectivelydisposed between the hollow shaft and the pulley at opposite ends of thehollow shaft, wherein the pair of thrust bearings are angularlydisplaceable relative to each other such that the hollow shaft isconstrained relative to the pulley and the piston is constrained toaxial motion when the pulley is rotated relative to the hollow shaft. 6.The torsional pulse dampener of claim 5, further comprising a secondspring disposed between one of the pair of angular thrust bearings andan end of the piston opposing the first spring to preload the pair ofthrust bearings against each other.
 7. The torsional pulse dampener ofclaim 1, wherein the first spring comprises a spring rate sufficient toallow at least one-half revolution of an angular differentialdisplacement between the pulley and the piston while a torque is appliedto the pulley and a counter-torque is applied to the hollow shaft. 8.The torsional pulse dampener of claim 7, wherein the spring rate issufficient to allow at least one revolution of angular differentialdisplacement between the pulley and the piston while a torque is appliedto the pulley and a counter-torque is applied to the hollow shaft. 9.The torsional pulse dampener of claim 1, further comprising a housingadjacent the pulley, wherein one of the one or more rotary bearings isdisposed between the pulley and the housing such that the pulley isrotational relative to the housing.
 10. The torsional pulse dampener ofclaim 9, further comprising one-way inlet valves disposed at one end ofthe hollow shaft along its interior surface.
 11. The torsional pulsedampener of claim 1, wherein one of the one or more rotary bearings isdisposed between the hollow shaft and the pulley at one end of thehollow shaft, and wherein the torsional pulse damper further comprisesan oil seal at the end of the hollow shaft exterior to the one rotarybearing.
 12. The torsional pulse dampener of claim 1, further comprisinga second spring arranged along a third portion of the hollow shaftadjacent an opposite end of the piston to which the first spring isarranged.
 13. A power plant comprising: an engine; a first pulleycoupled to a crankshaft of the engine; a pump coupled to an engineintake manifold of the engine; a drive shaft coupled to the pump; acontinuous variable transmission coupled to the drive shaft; a torquepulse dampener arranged exterior to the continuous variable transmissionand coupled to a rotating element of the continuous variabletransmission, wherein the torque pulse dampener comprises: a secondpulley; a piston that is axially displaceable within the second pulleyby rotational movement of the second pulley, wherein the second pulleyis moveably engaged with threads extending along an exterior surface ofthe piston to a full extent of axial displacement of the piston; ahollow shaft coupled to the piston via matted splines extendinglongitudinally along an exterior surface of the hollow shaft and alongan interior surface of the piston; and a spring arranged along a portionof the hollow shaft adjacent the piston to provide axial restraint ofthe piston, wherein the spring comprises a spring rate sufficient toallow torsional compliance from the engine for at least one-halfrevolution of an angular differential displacement between the secondpulley and the piston while a torque is applied to the second pulley anda counter-torque is applied to the hollow shaft; and a belt looped overthe first and second pulleys.
 14. The power plant of claim 13, whereinthe second pulley is rotationally coupled to the piston with a ballscrew or buttress threads.
 15. The power plant of claim 13, wherein thetorque pulse dampener is coupled to an output shaft of the continuousvariable transmission, wherein the hollow shaft is coupled to the outputshaft via a splined connection.
 16. The power plant of claim 13, whereinthe continuous variable transmission is a planetary ball continuousvariable transmission.
 17. The power plant of claim 13, wherein thedrive shaft passes through the hollow shaft of the torque pulsedampener.
 18. The power plant of claim 13, wherein the torque pulsedampener further comprises one or more rotary bearings disposed withinthe torsional pulse dampener such that the piston is axially displacedalong the hollow shaft by rotation of the second pulley.
 19. The powerplant of claim 13, wherein the engine is a one-cylinder engine.
 20. Thepower plant of claim 13, further comprising an additional transmissioncoupled to the engine or to the continuous variable transmission. 21.The power plant of claim 13, wherein an output shaft of the continuousvariable transmission passes through the hollow shaft of the torquepulse dampener.
 22. The power plant of claim 13, wherein the spring rateis sufficient to give torsional compliance from the engine for at leastone revolution of an angular differential displacement between thesecond pulley and the piston while a torque is applied to the secondpulley and a counter-torque is applied to the hollow shaft.
 23. Thepower plant of claim 13, wherein the spring rate is sufficient to givetorsional compliance from the engine for at least two revolutions of anangular differential displacement between the second pulley and thepiston while a torque is applied to the second pulley and acounter-torque is applied to the hollow shaft.
 24. The power plant ofclaim 13, wherein the spring rate is sufficient to give torsionalcompliance from the engine for at least three revolutions of an angulardifferential displacement between the second pulley and the piston whilea torque is applied to the second pulley and a counter-torque is appliedto the hollow shaft.
 25. The power plant of claim 13, wherein the hollowshaft of the torque pulse dampener is coupled to an input shaft of thecontinuous variable transmission via matted splines extendinglongitudinally along an exterior surface of the input shaft and along aninterior surface of the hollow shaft.
 26. A device, comprising: acontinuous variable transmission; and a torque pulse dampener arrangedexterior to the continuous variable transmission and coupled to arotating element of the continuous variable transmission, wherein thetorque pulse dampener comprises: a hollow shaft unimpededly encirclingan output shaft of the continuous various transmission; a pistonencircling a first portion of the hollow shaft, wherein the pistoncomprises a second set of splines extending longitudinally along aninterior surface of the piston, wherein the second set of splines ismated with a first set of splines of the hollow shaft; a first springarranged along a second portion of the hollow shaft adjacent the piston;a pulley encircling and coupled to the piston such that the piston isaxially displaced along relative to the pulley by rotation of thepulley; and one or more rotary bearings disposed within the torsionalpulse dampener such that the piston is axially displaced along thehollow shaft by rotation of the pulley.
 27. The torsional pulse dampenerof claim 26, wherein the one or more rotary bearings comprise a pair ofangular thrust bearings respectively disposed between the hollow shaftand the pulley at opposite ends of the hollow shaft, wherein the pair ofthrust bearings are angularly displaceable relative to each other suchthat the hollow shaft is constrained relative to the pulley and thepiston is constrained to axial motion when the pulley is rotatedrelative to the hollow shaft.
 28. The torsional pulse dampener of claim26, wherein the first spring comprises a spring rate sufficient to allowat least one-half revolution of an angular differential displacementbetween the pulley and the piston while a torque is applied to thepulley and a counter-torque is applied to the hollow shaft.
 29. Thetorsional pulse dampener of claim 26, further comprising a second springarranged along a third portion of the hollow shaft adjacent an oppositeend of the piston to which the first spring is arranged.
 30. A torsionalpulse dampener comprising: a hollow shaft comprising a first set ofsplines extending longitudinally along an exterior surface of the hollowshaft; a piston encircling a first portion of the hollow shaft, whereinthe piston comprises a second set of splines extending longitudinallyalong an interior surface of the piston, and wherein the second set ofsplines is slidingly mated with the first set of splines; a first springarranged along a second portion of the hollow shaft adjacent the pistonto provide axial restraint of the piston; a pulley encircling at least aportion of the piston, wherein the pulley comprises a recirculating ballsystem to axially displace the piston relative to the pulley by rotationof the pulley, and wherein the piston acts as a ball nut for therecirculating ball system; and one or more rotary bearings disposedwithin the torsional pulse dampener such that the piston is axiallydisplaced along the hollow shaft by rotation of the pulley.
 31. Thetorsional pulse dampener of claim 30, wherein the one or more rotarybearings comprise a pair of angular thrust bearings respectivelydisposed between the hollow shaft and the pulley at opposite ends of thehollow shaft, wherein the pair of thrust bearings are angularlydisplaceable relative to each other such that the hollow shaft isconstrained relative to the pulley and the piston is constrained toaxial motion when the pulley is rotated relative to the hollow shaft.32. The torsional pulse dampener of claim 30, wherein the first springcomprises a spring rate sufficient to allow at least one-half revolutionof an angular differential displacement between the pulley and thepiston while a torque is applied to the pulley and a counter-torque isapplied to the hollow shaft.
 33. The torsional pulse dampener of claim30, further comprising a second spring arranged along a third portion ofthe hollow shaft adjacent an opposite end of the piston to which thefirst spring is arranged.